Mechanical Engineering Journal (Dec 2014)
Numerical simulation of mechanical sensors using hydrated IPMCs
Abstract
The present study introduces the numerical simulation of mechanical sensors using IPMCs (ionic polymer-metal composites). IPMCs can be applied into both of actuators (from electricity to deformation) and mechanical sensors (from deformation to electricity), but the existing models of the actuators cannot be inversely applied to the mechanical sensors. The mechanical sensors generate very much smaller electric potential compared to the supplied electric potential of actuators with respect to the same displacement and structure. The non-invertible response of the mechanical sensors is numerically simulated, and the simulation considers hydration and transient behaviors. IPMCs have hydration effect that volume and mechanical stiffness are significantly changed with water uptake. In order to consider the volume swelling due to hydration, the total strains and pore pressure of IPMCs are respectively decomposed into stress-induced and hydration-induced parts. The hydration-induced strain is considered as eigen-strain, and the stress-induced strain and stress-induced pore pressure are employed into Biot poroelastic constitutive equations. The mechanical stiffness of a hydrated IPMC is expressed as empirical relations with water uptake. Furthermore, mechanical sensors using IPMCs show transient response with the relaxation and time lag of reaction force and electric potential. The transient response is modeled with a set of basic equations, e.g. layered Timoshenko beam model, Biot poroelastic model, Darcy-flow model, Poisson-Nernst-Plank model. The instantaneous peak of reaction force is estimated on undrained condition, the relaxation of reaction force is considered with pore pressure and its Poisson effect, and hydration-induced water migration is modeled with hydration potential. The hydration potential is modeled with an empirical chemical potential at free swelling equilibrium and is expressed as a function of water uptake. Next, discretization and numerical formulation with layered finite beam elements is introduced. Lastly, the transient responses of a Flemion-based mechanical sensor are numerically simulated with different deflections, and the distributions of stress, pore pressure, ion concentration and electric potential are obtained with time. Lastly, the numerical simulation is compared with the experiments of a reference.
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